bad full-wave rectifier?

[Nigel Goodwin]

Thanks for the help I just ended up buying everything from Mouser and I just ended up getting a ESD strap as well just to add on the order.

So now that I know with what's bad how does one blow the MOSFET in something like this?

It's a common failing, MOSFET's aren't particularly reliable, even less so than transistors in output stages.

But to be fair, the output devices are under a lot of strain.

 

[1-3-2-4]

I don't know if it ever worked when we moved to this new building.. So anything I can do to better protect it? I've heard of people having them repaired and maybe having them blow out again maybe 6 months later.

The stuff should be here on the 6th

 

[unclejed613]

this is very similar to a JBL sub model i see quite often. replace the 10uf/100V bipolar caps. they are probably dried out, and a likely cause of the MOSFETS running too hot.

while you are at it, replace the electrolytics next to the regulator transistors on the main board (i'm guessing if this is as much like the JBL as it looks, it's hidden behind the amp module shown in post#3)

 

[1-3-2-4]

I gotta try and find my probe for my meter but I'm curious to see the temp of the heatsink when its running..Not sure why they did not go with a external setup..

If it is indeed too hot is it possible to connect an AC fan to the rectifier?

 

[unclejed613]

my mistake, the board layout of everything except the amp module is a bit different than the JBL, so the regulator transistors are off to the extreme right somewhere, but there should be some 35V caps near them that are probably dried out.

actually the air motion in a powered sub is provided by the woofer itself, and no fan is required (and the noise it would make would be undesirable anyway, let alone the fan wouldn't be able to handle the pounding from the woofer, which is also why a lot of components are glued to the board)

 

[1-3-2-4]

I don't think noise is going to be an issue at all since it's in a place with 8 speakers

shoot I still can't find the probe for my DMM so I might need to use the IR gun

having said that the stuff that was on the backside of the FET's looked just like normal heatsink grease which I guess should be ok?

the real test is this other amp that needs work.. It's a crown.. when you turn it on it just flashes fault and never turns on.

 

[1-3-2-4]

Iron warmed up

Time to get this show on the road

Also since I had already ordered that full wave bridge I'm just going to go ahead and install that as well.

**broken link removed**
**broken link removed**

I just got one small question...

How are the FET's isolated?? The heatsink has little pads that go on the back of the MOSFETS however they seem to be made of metal as well.. The screws on the backside screw in.

You can't really see it but you can see in the picture the holes between the center MOSFET on the left and right

**broken link removed**

*edit nevermind ceramic insulators

 

[1-3-2-4]

It's fixed!!

Thanks you everyone here that helped! It sounds great but yeah I think for sure it was overdriven hard because it does sound good but I think the other guy tried to squeeze a bit too much from it.. Also I don't see much heat at all.. the heatsink is screwed onto the metal plate which again is like a larger heatsink.. I hardly see it over 76 F

Now I've got a crown amp to work on.. that's not going to be as easy as this I think

 

[michaeleleanor]

HI everyone, I just want to re-confirm if the amplifier used in ev sxa180 is similar to the amp used in boston hps 10 ho subwoofer as mine is not working i have figured out the problem is q10, q10b and Q11 may be the problem as they have been disfigured because of the heat, can some one guide me on this. Thanks

 

[unclejed613]

transistors don't usually get "disfigured" from heat unless they smoked, which burns the epoxy case from the inside. pictures?

 

[1-3-2-4]

Mine looked normal it was when I took the Mosfets out did I see all 3 were shot with a SC

 

[michaeleleanor]

View attachment 64387

 

[michaeleleanor]

View attachment 64388

 

[michaeleleanor]

This is the image of the amplifier of boston hps 10 ho subwoofer, which is 250 watts unlike sxa-180 which is 300 watts.
I find the output transistors to be short q11 / q 10 / q10b . The part number cannot be read because of the over heat or may be the manufactured has scraped them, so that cosumer come to them for repair.
To cut it short I just need to know whether I can use the same output transistors of sxa-180

 

[michaeleleanor]

View attachment 64389

 

[michaeleleanor]

any reply would be aprreciated.

 

[alec_t]

To cut it short I just need to know whether I can use the same output transistors of sxa-180

Without the schematics of both amps, or the knowledge of someone experienced with both amps, it's impossible to say. You could take a chance. Are you feeling lucky?

 

[michaeleleanor]

View attachment 64414

 

[michaeleleanor]

HI Alec, if you see the image that I had posted, it is very similar to sxa -180. I managed to get the description of Q10 which is IRF 9640 and did further search and found the same mosfet irf 9640 at location Q 10 in the infinity subwoofer schematic which is attached above, with the help of this schematic what i understand the part number of Q10 and Q 10b will be similar which is IRF 9640 and q11 is IRF640. I WILL GO AHEAD WITH THIS AS I JUST CAN'T FIND THE SCHEMATIC OF HSP 10HO BOSTON SUBWOOFER

 

[unclejed613]

a lot of the mosfets used these days don't have the numbers printed on them in ink anymore. the numbers are laser etched in the surface, and can be hard to read. rubbing some white heat sink grease into the lettering and wiping off the excess makes them easier to read.